The HA argument makes sense, but I don't think that would need 2.4GHz and 5GHz traffic to be separated.
That is indeed what happens when LAGing for capacity, but keep in mind that 1Gbps (full-duplex) Ethernet capacity is more than enough to carry traffic from this AP in realistic use-cases and deployments. While the AP-335 can demonstrate up to ~1.5Gbps (unidirectional) L3 traffic in a lab setting, this will remain well below 1Gbps in a typical use and deployment (RF channel conditions, client mix and capabilities, etc.). And that's assuming you're using 80MHz (or 160MHz) channels, while most deployments are using 40MHz.
I'm not very familiar with LAG/LACP configuration, but would expect that for an active/standby HA use case, the traffic from both radios will not be separated.